1. Field of the Invention
This present invention relates to image data filtering, and more particularly to an improved algorithm for reducing ringing noise in image/video coding. The invention, which can be embodied in an apparatus, methods or programs of instructions, is particularly well suited for highly compressed image/video coding.
2. Description of the Related Art
Most of today's video coding standards, such as MPEG-4 of the International Organization for Standardization (ISO) and International Telecommunication Union (ITU) H.263, adopt block-based motion compensation and perform a discrete cosine transform (DCT) operation on the blocks. In the case of still image coding, using JPEG, the block-based DCT coding is also adopted. When an image is highly compressed, the block-based coding may cause blocking artifacts and ringing noise. A typical blocking artifact is grid noise in a homogeneous area in which adjacent pixels have relatively similar pixel values. Ringing noise, which is most noticeable near real edges, occurs as a result of Gibb's phenomenon due to the truncation of the high frequency coefficients by quantization. Ringing noise is also called “mosquito noise,” as it often occurs at a boundary areas between a human skin regions and background, and thus visibly resembles mosquitoes flying around a person's head and shoulders.